Ok, first off Onkyo is a VERY good company, they make good quality stuff (good chioce). Second that is not an amplifier, its a reciever, there is a difference. AMPs ONLY amplify, there is no tuner and usually no volume, and it would need to be hooked up to a non amplified reciever. Reciever have the amplifier integrated into them, they have volume, bass/treble controls, and source controls (tape,tv,aux,etc.). Now that we got that straight, heres how you run it. First off your going to need an adapter that has 2 "headphone" style connectors (forgot the technical name) to RCA cable ends. Basically, youd hook the the headphones jacks into your comp run it to the input of your choice (tv,cd,dvd,etc), then you run your speakers off of the reciever. You cant run computer speakers off of this. You need regular house speakers with an 8ohm impedence. I believe that computer speakers have maybe a 1 or 2 ohm impedence. This means that if you choose to run your comp speakers off of this reciever I can alsmot guarantee youll blow em the first time you put power to them. And yes you can hook the 5.1 or 7.1 to the reciever but it wont matter as the reciever has its own pro logic (whatever) built in to it. So youd probably have to set your sound card to 2.1 and let the reciever do the actual 5.1,7.1 splitting.
-P.